Tapping Aluminium extrusion

[Jonathan]

Could you grind a non-cutting cylindrical portion on the end of the tap the same diameter as the pilot hole? That should ensure the tap stays on center.

[Jonathan]

Had another idea...could you make a mild steel bushing piece that fits on the end of the extrusion with a tapped hole over where you want to tap. Clamp it to the end then try tapping it using the tapped hole to guide the tap initially? Hope that makes sense!